Thin film magnetic heads are well known and widely employed in the art of visual and sound reproduction.
A typical thin film magnetic head is illustrated in the drawing in which 1 is a substrate, 2 a protective layer, 3 represents each of three separate insulation layers, 4 a magnetic layer, 5 an adhesive layer and 6 a coil layer.
For maximum efficiency, the substrate layer should have high abrasion resistance and good lubricity. For optimum mechanical strength the coefficient of thermal expansion of the substrate and the magnetic layer should be approximately equal. Moreover, since an electric current is passed through the thin film magnetic heads, there must be good thermal conductivity so that the magnetic characteristics of the head are not affected by changes in temperature.
A wide variety of known materials are now employed in the preparation of magnetic heads. For example ferrite with a thermal expansion of 1.times.10.sup.-5 /.degree.C. is often utilized in the preparation of substrates because of its good abrasion resistance. Other materials employed in the preparation of substrates include ceramic glass (coefficient of thermal expansion: 1.times.10.sup.-5 /.degree.C., thermal conductivity: 2 k cal/m.hr..degree.C.), and silicone (coefficient of thermal expansion: 5.times.10.sup.-2 /.degree.C., thermal conductivity -60 k cal/m. hr. .degree.C.). There are no known materials which are totally satisfactory for the preparation of substrates taking into consideration all properties which would be desirable in substrate components. As a result, substrates are presently prepared utilizing materials representing compromises between what the art wishes to achieve and what can actually be achieved.